Fix compile error with Z_PROBE_END_SCRIPT (#14447)

Marlin/src/feature/bedlevel/ubl/ubl_G29.cpp

       if (DEBUGGING(LEVELING)) DEBUG_ECHOLNPAIR("Z Probe End Script: ", Z_PROBE_END_SCRIPT);
       if (probe_deployed) {
         planner.synchronize();
-        process_subcommands_now_P(PSTR(Z_PROBE_END_SCRIPT));
+        gcode.process_subcommands_now_P(PSTR(Z_PROBE_END_SCRIPT));
       }
     #endif